Ignition system



March 11, 1952 II III? T. TOGIOLA 2,589,164

IGNITION SYSTEM Filed May 8, 1950 I N VEN TOR.

19M a. 6m

ATTORNEY.

Patented Mar. 11, 1952 IGNITION SYSTEM TullioTognola, Sidney, N. Y., assignor to Bendix Aviation Corporation, New York, N. Y., a corporation of Delaware Application May 8, 1950, Serial No. 160,744

9 Claims. 1

This invention relates to electrical: apparatus and more particularly to apparatus for producing electrical spark discharges, such as those adapted {or use in systems for igniting combustible charges in various types of internal combustion engines and so-called jet or turbine engines of the direct expansion type.

One of the objects of the invention is to provide novel electrical apparatus which is of light weight in comparison to prior apparatus adapted for similar purposes and which requires only a minimum of space for installation.

Another object of the invention is to provide a novel electrical apparatus of the above character wherein'no mechanically driven parts are required.

Another object is to provide a novel electrical system for producing high-energy, high-frequency spark discharges at relatively low voltage across aspark gap of practical dimensions.

A further object is to provide a novel ignition 'systemfor combustion engines or the like where- 'ina relatively low voltage is employed so that electrical losses are minimized, the possibility of electrical failures is materially reduced, and the requirements for radio shielding are greatly simplified.

A still further object is to provide an ignition circuit of the above type which is reliable in operation at'all altitudes and under adverse conditions which would cause certain failure of known types of systems.

The above and further objects and novel features'of the invention'will more fully appear from the following detail description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of "the limits of the invention.

fInthe drawings, Fig. 1 is a diagram of one form of electrical circuit embodying the present inven- The single embodiment of the invention illustrated by way of example in the accompanying =d'rawingsisin a form-adapted for use as the ignition systemot a so-called jet-type engine. As shown, 's'a'id s ystem comprises a suitable source of electrical energy which may be a battery It adaptedito'be' connected to the remainder of the circuit through a switch 9 and a ground or equivalent' connection. However, other known types of sources of electrical energy may be used either simultaneously or alternatively with or in lieu of :thebattery. Byway of example, a storage bati QW 'OI-the type having -a-z l-volt rating and capable of delivering about 30 volts may be used. In installations where the source supplies other circuits, suitable filtermeans I i are provided to pre vent radio frequencies from feeding back into the battery circuits. The particular filtering means shown comprises three by-pass condensers connected between ground and the power supply line I5 in which there is an inductance 12, but other known types of filters may be used, and in some installations none is necessary.

The voltage of the source is stepped up to the desired voltage by means of a suitable transformer 13, the primary winding i l of which is preferably connected to the power or supply line [5 through a variable resistor 15. The other end of said rimary winding is adapted to be alternately connected to and disconnected from ground or the low-potential terminal of the source by means of a vibrator IT to be more fully hereinafter described. The interrupted current flow through the primary winding is effective to induce a higher voltage in secondary winding It, the high potential terminal of which is connected to a storage condenser 19 through one or more rectifiers 20. The rectifier means may be of the gaseous tube type or of any other suitable known type adapted for passing energy of selected polarity to condenser 39 and for blocking its return flow from the condenser to the transformer.

One terminal of condenser is is connected to ground and the other terminal, in addition to being connected to rectifier 20, is connected through a control spark gap 2| to the insulated terminal or electrode 22 of a spark gap device 23, the other electrode 24 of which may be connected through ground or by direct connection to the low potential terminal of condenser l9. For a purpose to more fully appear hereinafter, the spark gap between electrodes 22 and 24 is bridged by a high resistance element 25/ The latter element makes electrical contact with both electrodes 22 and 24 but oifers very high resistance to the flow of electrical current. The device 23 may be in the form of a spark plug or igniter of the types disclosed in co-pending'applications Serial No. 98,093, filed June 9, 1949, for Electrical Apparatus and Serial No. 160,762, filed May 3, 1950, for Electrical Apparatus. The control spark gap 21 is preferablyof the sealed type and is constructed to break down or become conductive at substantially the same voltage under all operating conditions. One suitable type'is disclosed in Linkroum et al. application Serial No. 107,314, filed July 28, 1949, for Spark Gap now patent No. 2,540,399.

The vibrator or interrupter for interrupting the .flowof current from battery ID or other direct current source through winding I4 of the transformer may be of any suitable known construction and as shown comprises a stationary contact a connected to the low potential end of primary winding I4. A second stationary contact b is connected through a current limiting resistor 29 to power line I5. A flexible conductive reed 21 or the equivalent thereof is connected to ground at 28 and is adapted to be flexed upwardly into engagement with contacts a and b. Upward flexing of the reed may be effected by an electro-magnet, the coil 29 of which is connected at one end to the battery through resistance 2'5 and at the other end to ground at 23 through a lead 30. Another stationary contact c connected to winding M and engageable by reed 2'! when the latter is flexed downwardly, as viewed in the drawings, may be provided for doubling the frequency of the current fluctuations in the transformer. A condenser 3I may be shunted across reed 21 and contacts a and c to prevent arcing at these contacts.

To place the above system in operation the ignition switch 9 is closed, whereupon current flows through power line I5, resistance 26, coil 29 and lead 39 to ground at 28. The energized coil 29 electro-magnetically attracts reed 21 upwardly into engagement with contacts a and b. The engagement at contact a closes a circuit from the battery ID to ground at 28 through variable resistance I6 and primary winding I4. gagement at contact b eifects a low resistance shunt across coil 29 so that the latter becomes ineffective to electromagnetically hold reed 21. When the latter is released, it disengages contacts a and b and swings downwardly past its normal position midway between contacts a and into momentary engagement with contact 0, thereby again closing the circuit through winding I4. The disengagement of reed 2'! and contact b re-establishes the flow of energy to coil 29 and again renders it effective to attract the reed into re-engagement with contacts a and b. This series of events is automatically repeated in rapid succession at a frequency determined by the design of the vibrator in a manner well understood in the art.

The flow of interrupted current through winding I4 is effective in a known manner to induce a voltage across secondary winding I8. This induced voltage may be many times greater than the voltage of the source, depending upon the design of the transformer, and is preferably sufficient to build up a charge of not materially less than 3000 volts on condenser I9 in the system shown. It will be understood that the open circuit voltage available at secondary winding I8 will be determined by the transformer ratio and the self induced voltage across primary winding I4 when the circuit therethrough is interrupted at the vibrator. Energy from winding I8 is delivered in increments through rectifiers 29 to condenser I 9 and is accumulated or stored in the condenser until the voltage across the same attains the breakdown voltage of control gap 2|, preferably not less than about 3000 volts. half-wave or uni-polarity rectifiers 20 pass current in only one directionand hence prevent the leakage of energy from condenser I9 back to the transformer.

When the voltage across condenser I9 has been built up to the predetermined break-down voltage of control gap 2I the latter becomes conductive and effectively connects the condenser to igniter 23. The normal break-down voltage of the spark gap between electrodes 22 and 24 The en- I The is materially greater than the voltage to which the condenser is charged, but the condenser dis charges a small amount of energy through or alongv the surface of resistor 25. This flow of energy is effective to ionize the gaseous medium of the gap between electrodes 22 and 24 thereby reducing the resistance of said medium so that condenser I9 will discharge across the same and create an arc of very considerable energy at relatively low voltage. The spark gap 2224 may be of such width that a voltage of over 4000 volts would be required to bridge it at atmospheric pressure in the absence of resistor 25. p

The sparking rate at gap 23 may be determined with a reasonable degree of accuracy by properly designing the various elements of the system, such as the vibrator, transformer, rectifiers, etc. The variable resistor I6 is provided for the purpose of varying the sparking rate and may be used to correct or compensate for production tolerances and the like. It will be understood, of course, that the sparking rate will vary with changes in the source voltage, but this variable may be countered or reduced to a substantial extent by properly designing the transformer I3 in the light of the known variation in source voltage. This is accomplished by designing the transformer to operate at the available voltages along the so-called knee of the magnetization curve of the transformer core which may be of the air-gap type to thereby ive good energy transfer without excessive variation.

In one suitable embodiment designed for use in igniting jet or turbine type engines the source of energy consists of a battery having a 24-volt rating and capable of delivering voltages varying between 14 and 30 volts during operation. The resistances I6 and 26 are 2.6 ohms and 15 ohms, respectively, and the primary and secondary windings of the transformer consist of turns of No. 29 enamelled copper wire and 8500 turns of No. 42 enamelled copper wire, respectively. Rectifiers 20 are commonly known as CK1013 rectifier tubes, and condenser l9 has a capacity of .15 microfarads. Control gap 2| has a break down voltage of approximately 3000 volts, and the spark gap between electrodes 22 and 24 is about .020 inch. These values are exemplary only and may be varied for difierent installations.

There is thus provided novel electrical apparatus which is capable of operation by a source of very low voltage to produce high energy sparks at a desired rate and at a voltage considerably lower than the normal spark-over voltage of the spark gap across which the sparks occur, but higher than the source voltage. Because of the relatively low maximum voltage employed and the manner in which it is generated, the system may be made small and light thereby adapting it for use on aircraft engines. Danger of operation failures from flash-overs and the like is also "tion, it is to be expressly understood that the in- 'vention is not limited thereto. For example other known'meansoiinterrupting current may be ployedinlieubfvibrator Hand ii "alternating --tui"ning the discharges of the' condenser to a plurality 'ofcdifferent 'sparking devices 23. In

some-installationsthe resistor 25 may consist of a tliin coating of an electrically conductive material onithe surface of a non-conductor. 'Various changes may also be made'inthe design and arrangement of the parts illustrated as well as in the materials, electrical values, and circuit constants herein suggested as suitable without departing from the spirit and scope of the invention as it will now be understood by those skilled in the art. For example, the various voltages, resistances, capacities, gap dimensions and the like must be chosen to suit a given circuit for producing the desired energy under the prevailing conditions of operation.

What is claimed is:

1. In an ignition circuit for combustion engines or the like, a storage condenser, a source of electrical energy for charging said condenser, a spark gap having a normal spark-over voltage in excess of the maximum voltage of the charge attainable by said condenser, an element having a high electrical resistance below the normal resistance of said gap connecting the electrodes of the latter,

and means including a second spark gap having a breakdown voltage not greater than said maximum voltage for connecting said first-named spark gap in circuit with said condenser, said resistance being capable of conducting successive discharges from said condenser to efiect ionization of said first-named spark gap and render the latter conductive to said condenser discharges.

2. In an electrical circuit, a storage condenser, a source of uni-polar electrical energy for charging said condenser, a spark gap having a normal spark-over voltage greater than the voltage of the maximum charge attainable by said condenser from said source, means including a control gap having a breakdown voltage not greater than said maximum attainable by said condenser for intermittently connecting the high potential terminal of said condenser with an electrode of said spark gap, and an electrical resistance element connecting said spark gap electrodes, said element being capable of conducting current between said electrodes during the initial discharge of said condenser whereby the spark-over voltage of the spark gap is momentarily reduced below the voltage of the charge stored on the condenser and a spark is created between said electrodes by the remaining discharge of said condenser.

3. An electrical circuit comprising a storage condenser, a spark gap comprising a pair of spaced electrodes, means including a control gap for connecting said spark gap in circuit with said condenser, said control gap having a spark-over voltage below the spark-over voltage of said spark gap, and means for causing said condenser to dis-- charge as an arc across said spark gap when the charge on the condenser reaches the spark-over voltage of said control gap, said last-named means including an electrical resistance bridging the electrodes of the spark gap.

"4; '=In' electrical apparatus of thecla'ss described; a condenser; a source of electrical-energy for chargingsaid condenser, a control gap anda spark gap in circuit with said condenser, said control gap having a normal spark-over voltage not-greater than thevoltage 'of the'charge attainable by said condenserandsaid-sparkgap having a normal spark-over voltage greater than the voltage-of the charge attainable by-saidcondenser, 'and means-for momentarily reducing the spark-over voltage of "the spark gap to permit,

saidcondenser to discharge as an arc across the 'samethrough-said control gap, said means includinganelement having surface contact with the electrodes of-said'spark gap and-bridging the latter atone edgethereof.

5. 'In apparatus of the class described, a storage condenser, means for charging said condenser including a battery and current interrupting means, a spark gap comprising spaced electrodes and having a normal spark-over voltage greater than the voltage of the charge supplied to said condenser, means including a control gap for connecting said spark gap in circuit with said condenser, said control gap having a spark-over voltage not greater than the voltage of the charge supplied to said condenser, and means for causing said condenser to discharge across said gap as an are including a semi-conductive element bridging the spark gap between said electrodes for initiating the flow of current therebetween in the absence of an are.

6. In apparatus of the class described, a storage condenser, a source of electrical energy for supplying uni-polar charge to said condenser, said source including a battery, a transformer coil having the primary winding thereof in circuit with said battery, an electro-magnetically operated circuit breaker for intermittently interrupting the circuit through said primary winding and means including a rectifier for connecting the secondary winding of the transformer to said condenser, a spark gap having a normal sparkover voltage greater than the voltage of the maximum charge supplied to said condenser by said source, means including a control gap for connecting said spark gap in circuit with said condenser, said control gap having a spark-over voltage not greater than the voltage of the maximum charge supplied to said condenser, and means for initiating the discharge of said condenser as an arc across said spark gap including a high electrical resistor connecting the electrodes of said spark gap.

7. Apparatus as defined in claim 6 wherein the charge on the condenser is built up in increments to the spark-over voltage of said control gap.

8. In an electrical circuit for creating a spark discharge, a direct current source of electrical energy, means including a transformer for stepping up the voltage of said source, a storage condenser connected to the secondary winding of the transformer, a control gap and a spark gap connected in series with said condenser, the normal breakdown voltage 01 said control gap being not greater than the voltage of the charge attainable by the condenser and the normal breakdown voltage of said spark gap being greater than the breakdown voltage of the control gap, and a resistor connecting the electrodes of said spark gap for conducting current from said condenser until the breakdown voltage of the spark gap is reduced to that of the charge on the condenser to permit the latter to are discharge across said electrodes.

9. Electrical apparatus of the class described comprising a direct current source of electrical energy such as a battery, a transformer comprising primary and secondary windings for stepping up the voltage of said source, electromagnetically operated vibrator means energized by said source for intermittently interrupting current flow from .said source through said primary winding, a storage condenser, means including rectifier means for operatively connecting said secondary winding to said condenser, a control gap having a substantially constant breakdown voltage for controlling the discharge of said condenser, and a spark gap connected to said control gap comprising spaced electrodes and a resistor connecting said electrodes in proximity to the gap therebetween whereby flow of electrical energy in said resistor ionizes the gaseous medium between said electrodes. and ..permits the condenser to arc discharge across'said electrodes. TULLIO TOGNOLA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

